1. Field of Invention
This invention relates generally to magnetic compasses, and more particularly to a compass that includes a rotatable pointer to indicate direction and a rotatable magnetic field detector that orients itself with respect to the earth's magnetic field and is so linked to the pointer that rotation of the detector produces a corresponding rotation of the pointer regardless of the degree to which the detector tilts as a result of the inclination of the magnetic field and the attitude of the compass with respect to the horizontal plane.
2. Status of Prior Art
A magnetic compass is a device for determining direction. In its traditional form, it consists of a magnetized needle supported for rotation within a capsule or casing having a transparent cover. The needle, which acts as a pointer, aligns itself with the earth's magnetic field, a scale marked in degrees serving to specify direction relative to this magnetic field. Modern compasses make use of iron alloys or ferrite magnets capable of permanently maintaining a strong magnetization.
In a magnetic compass, it is conventional to mount the needle on a pointed staff serving as a fulcrum, the point of the staff being received in a jewel bearing to minimize friction so that the needle is free to tilt as well as to rotate. Such compass needle mountings are disclosed in the Swiss patent CH 663091 to Recta (1987), the German patent 173,956 to Neufeldt and Kuhne (1906), the Japanese patent 58-129289 to Matsushita Denki Sangyo (1983), and the Swiss patent 32 8760 to Recta (1976).
A standard magnetic compass in which the magnetized pointer or needle is free to tilt as well as to rotate within a casing has serious drawbacks. Should the needle become angled relative to the top or bottom wall of the casing and the degree of tilt is such that the needle touches one of these walls, movement of the needle will be arrested, as a consequence of which an accurate reading of direction will not be obtained.
Tilting of the needle occurs, not only when the attitude of the compass deviates from the horizontal plane so that it is not level, but also when the compass is used in different latitudes of the earth. The earth's magnetic field has different inclinations at different latitudes, this causing the rotatable needle to more or less dip to a degree that depends on the prevailing inclination.
The term "magnetic field detector" as used herein refers to a rotatable device which incorporates in its structure one or more permanent magnets, so that the device rotates to orient itself with respect to the earth's magnetic field.